elastic properties of solids
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About elastic properties of solidsTRANSCRIPT
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-Elastic Properties of Solids -Elastic Properties of Solids
AP Physics CMrs. Coyle
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• Real objects are not rigid but can deform under the influence of an external force.
• Remember: Hooke’s Law F=-kx
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Elastic Properties of SolidsElastic Properties of Solids
• Length (Tensile Stress- Strain)
• Shape (Shear Stress-Strain)
• Volume (Bulk Stress-Strain)
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Elasticity of Length- CharacteristicsElasticity of Length- Characteristics
• Tensile Strain= L
L
Tensile Stress=F/A
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Elasticity in LengthElasticity in Length
• Tensile Stress = Y x Tensile Strain
• Y is known as Young’s Modulus• Units of Y are N/m2
F LY
A L
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Tensile Strength Test
• Tensile Strength Sample
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Ex: #30
• A steel wire of diameter 1mm can support a tension of 0.2kN. A cable to support a tension of 20kN should have a diameter of what order of magnitude?
• Ans: 1cm
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Elasticity in Shape - Shear Stress= F / A
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Example: Shear Stress
http://www.fema.gov/plan/prevent/earthquake/fema74/chapter2_2.shtm
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http://www.fema.gov/plan/prevent/earthquake/fema74/chapter2_2.shtm
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Shear Stress and Shear StrainShear Stress and Shear Strain
F xS
A h
S is the Shear Modulus,
Unit : N/m2
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Ex: #33
If the shear stress in steel exceeds 4.00x108 N/m2
the steel ruptures.
a)Determine the shearing force necessary to shear a steel bolt 1.00cm in diameter.
Ans: a) 3.14x104 N
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Ex: #33 cont’d
b)Determine the shearing force necessary punch a 1.00cm diameter hole in a steel plate 0.500cm thick.
Ans: b) 6.28x104 N
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Elasticity in VolumeElasticity in Volume
F VB
A V
B is the Bulk Modulus
Unit: N/m2
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• Note that ΔF/A is pressure.
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Ex:#35
When water freezes, it expands by about 9%. What pressure increase would occur inside
your automobile engine block if the water in it froze?
(The bulk modulus of ice is 2.00x109 N/m2 )
Ans: 1.65 x 108 N/m2
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Explaining the inertia ball tensions.
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• How is ΔL affected when you have two same springs in series or in parallel pulled by the same force?